This invention relates to hydraulically driven air-borne vehicles with plural propellers of vertical or inclined propeller-axes whereby the craft may take off and land vertically and fly either with inclined axes like a helicopter or also with stiffer inclined axes for high forward speed or even horizontal flight with substantially nearly horizontal propeller axes. This invention deals in particular with a common control of a pair of propellers to assure a clean straight forward flight path of the vehicle without departures from the forward flight path by controlling errors.